This invention relates in general to a plastic pallet. Specifically, this invention relates to a plastic pallet which is a general purpose shipping pallet formed from a thermoplastic material and assembled without any mechanical fasteners.
Shipping pallets are well known in the art. Pallets are typically made of wood and used for supporting various items. They are constructed to be handled with a forklift or similar lifting device within a plant, a warehouse, or loading dock. There are several disadvantages to wood pallets. These disadvantages include the weight of the pallet and their susceptibility to breakage during use. In addition, wood is subject to deterioration that occurs with age and exposure to weather. Wood is also subject to attack by insects, mold and bacteria. There is the potential for damage to the pallet caused by spills from the goods that the pallets are bearing, for example a chemical spill or even physical damage from heavy loads. As a result, pallets are often discarded at waste sites and landfills. Contaminated wood pallets may present potential environmental hazards. The limited availability of the natural resources used to make the wood pallets is also a concern in many parts of the world. Also, wood pallets are not very hygienic for food and medical applications.
Metal pallets are also available, but have several drawbacks including their expense, susceptibility to corrosion, potentially poor chemical resistance and weight. When corroded, metal pallets are not very hygienic for food or medical applications either.
There have been many attempts to produce plastic pallets which are available in numerous shapes and forms. Industry has looked to plastic as an alternative to wood or metal for a number of reasons including the superior chemical resistance of plastic over wood or metal, the hygienic quality of plastic over wood or metal, the weight advantage of plastic, and the fact that some configurations of plastic pallets are less expensive to manufacture. In addition, plastic provides a major uniformity and consistency advantage in material over wood.
U.S. Pat. No. 5,704,300 describes a plastic pallet which is held together with mechanical fasteners. U.S. Pat. Nos. 5,527,585 and 5,405,567 describe plastic molded load-bearing structures. These patents describe structures fabricated from usually dissimilar plastic materials such as a deck sheet with downward extending feet that may be made removable so as to have a snap fit attachment.
Other patents describing plastic pallets of particular shapes and designs include U.S. Pat. Nos. 5,456,189; 5,505,141; 5,197,395; 4,843,976; 4,482,051 (Re32,530); U.S. Pat. Nos. 4,051,787; 3,989,156; 4,809,618; 4,799,433; 3,938,818; 3,938,448; 3,835,792; 3,702,100; 3,700,205; 3,610,172; and 3,603,272. The foregoing patents describe the advantages of a plastic pallet over the prior art wood pallet and describe pallets of various designs and shapes as well as methods for forming them.
Another approach has been to provide plastic laminates or panels such as taught in U.S. Pat. No. 5,219,629. Alternately, there have been attempts to make composite structural systems from plastics or some other reinforced composite material as described in U.S. Pat. Nos. 4,230,049 and 5,435,954. Other patents of interest that teach and describe fabricating or molding various shapes using plastic material include U.S. Pat. Nos. 5,547,081; 5,312,858; 5,259,169; 5,238,633; and 3,917,108.
U.S. Pat. No. 3,878,796 describes a plastic pallet assembly which includes boards and stringers that are held in an interlocked relationship with an arrangement of integral notches and shoulders.
There still exists a need for a plastic pallet that is simple in construction and easy to fabricate that has load bearing capability at least comparable to a wooden pallet. The plastic pallet would preferably have extruded thermoplastic members which are economical and lightweight. Advantageously, the extruded members include thermoplastic deck boards and stringers which provide design flexibility in fabricating pallets of various configurations and sizes. The plastic pallet may include stringers that have end caps that seal the ends of the extruded profiles and which provide added strength and durability. Preferably, the pallets would be constructed of a thermoplastic material that allows for a long useful life and complete recycling. The plastic pallet preferably would be constructed using a joining technology that does not require mechanical fasteners. Preferably such a plastic pallet would include ridges or other non-slip members on its deck boards and/or stringers. The ridges or other members may function to reduce slippage. The ridges may also function as energy concentrators for welding, may provide adhesive gap control when adhesives are employed as the joining technology, and may serve as mechanical interlocks during pallet storage and shipment. Preferably, the plastic pallet configurations may allow either four-way fork entry or two-way fork entry by a forklift or hand truck to facilitate stacking, lifting, and handling of the pallet. The profiles of the deck boards may in some embodiments include chamfers at desired locations for facilitating fork entry and exit from the pallet.
It is an object of the present invention to provide a plastic pallet that is constructed of a thermoplastic material capable of being reused and recycled.
It is a further object of the present invention to provide a plastic pallet having deck boards with ridges so as to reduce slippage, to act as an energy concentrator for welding, to provide adhesive gap control when adhesives are used for the joining technology, and/or to provide interlocks during pallet storage and shipment.
It is a further object of the present invention to provide a plastic pallet that is extruded so as to be less expensive and lightweight, and still exhibit sufficient load bearing capacity.
It is a further object of the present invention to construct the plastic pallet with a joining technology that does not require any mechanical fasteners so as to minimize potential tear points and to allow for direct recycling.
It is a further object of the present invention to provide a plastic pallet constructed from extruded profiles that offer design flexibility for making a wide variety of pallets in various sizes and shapes.
It is a further object of the present invention to provide a plastic pallet produced in a block style with four way fork entry.
It is a further object of the present invention to provide a plastic pallet with deck boards that have a chamfer at desired locations.
It is a further object of the present invention to provide rib reinforced deck boards and stringers for a plastic pallet.
It is a further object of the present invention to provide an automated process for constructing a plastic pallet of a variety of designs from basically two building blocks, the deck boards and stringers.
It is a further object of the present invention to provide a plastic pallet having deck boards and stringers constructed of different thermoplastic materials for providing a desired degree of toughness, rigidity, and durability.
It is a further object of the present invention to provide a plastic pallet that can include a variety of shock absorbers for improving impact strength including but not limited to bumper strips on edge boards, resilient blocks between boards, and/or semi-rigid or flexible end caps.
It is a further object of the present invention to provide a plastic pallet constructed for operation with either two-way or four-way fork entry for facilitating loading and stacking of the pallets.
It is a further object of the present invention to provide end caps for the stringers and the deck boards for reducing areas of contamination by bacteria, fungi, mold, insects, dirt, and the like.
It is a further object of the present invention to provide a plastic pallet that includes removable end caps for the stringers to provide additional compartments for identification purposes, or to provide variable weight to control the stability of the pallet and the material thereon.
It is a further object of the present invention to provide a plastic pallet with end caps that include identifying means such as a bar code, processor chips, or the like.
It is a further object of the present invention to provide a plastic pallet which is simple in design, rugged in construction, and economical to manufacture.
It is a further object of the present invention to provide deck boards with surfaces that exhibit greater traction and resistance to slippage through the use of features which resist movement such as dimpled surfaces, sinusoidal shaped ridges, intermittent ridges across boards, non-slip members or a co-extruded layer of high coefficient of friction as a surface layer.
It is a further object of the present invention to provide a plastic pallet that includes ridges on the stringers to facilitate construction of a pallet held together by hot plate welding.
Further objects of the present invention will be made apparent following the Best Modes for Carrying Out Invention and the appended claims.
The foregoing objects of the present invention are accomplished by a plastic pallet. The pallet is constructed of a plurality of longitudinal spaced apart stringers having deck boards joined thereto without mechanical fasteners. Each of the stringers are formed from a thermoplastic material and in cross section have a pair of longitudinal walls connected by a top surface and a bottom surface. Each of the stringers includes an interior area defined by the walls and the top and bottom surfaces. Each of the stringers further has at least one and preferably a plurality of reinforcement ribs extending in the interior area thereof The reinforcement ribs preferably have radiused corner surfaces where they join the walls or top and bottom surfaces. The ribs preferably include ribs having an orientation substantially perpendicular to the longitudinal walls.
A plurality of longitudinal spaced apart deck boards also formed of a thermoplastic material are situated transversely on the stringers. Each of the deck boards includes in cross section an upper side and a lower side connected with side walls through radiused corners. The sides and walls define an interior area. A plurality of reinforcement ribs are situated in the interior area. The ribs also preferably include radiused corner surfaces where they join the sides and walls. The ribs have a preferred direction that is substantially perpendicular to the upper and lower sides. Preferably, the deck boards include ridges on the upper and lower sides thereof. The ridges may serve to reduce slippage, provide a better bonding surface and adhesive gap control, and/or act as energy concentrators for welding the deck boards to the stringers. The ridges may also function as physical interlocks during pallet storage and shipment. Deck boards are joined to the top surfaces as well as on the bottom surfaces of the stringers to provide a pallet structure having sufficient load bearing capacity. Preferably, the deck boards are positioned adjacent the ends of the stringers with the edges of the side walls of the stringers generally aligned with the ends of the stringers, or with the face of end caps which may be positioned on the ends of the stringers.
In an alternate embodiment according to the present invention, the stringers include a plurality of ridges on their top and bottom surfaces. The ridges may facilitate attachment to the deck boards when they are joined with hot plate welding. Alternatively, the top and bottom surfaces of the stringers may include other suitable features to enhance engagement of the boards and stringers.
The plastic pallet in accordance with the present invention may optionally include removable end caps for the stringers and/or deck boards. The end caps preferably seal the interiors of the stringers and deck boards against contamination and damage. The end caps may also include an identification means for identifying the pallet or the material supported on the pallet, such as a bar code, processor chips, or other identifying indicia.
Alternative embodiments of the invention may include end caps for the stringers which help maintain structural integrity and increase durability of the pallet. The end caps preferably close the interior area of the stringers at each end. The end caps preferably include projecting portions which extend adjacent to and in fixed engagement with the longitudinal walls and/or the top and bottom surfaces of the stringers. The projecting portions extend in engagement with the walls or surfaces a substantial distance inwardly from the end of the stringer to provide reinforcement in the end area. Such reinforcement helps to minimize damage due to engagement of the end caps and stringer ends with the forks of lift and hand trucks. The projecting portions of the end caps may extend externally or internally of the stringers. The end caps may be fixed to adjacent deck boards as well as to the stringers.
Advantageously, the stringers in plastic pallets made in accordance with the present invention are configured to provide openings to allow for either two-way fork entry or four-way fork entry, that is entry to the pallet in either direction for lifting and moving the pallet, with a hand truck or forklift. The plastic pallets made in accordance with the present invention are preferably constructed with a joining technology that does not require mechanical fasteners. This may be achieved through use of attachment methods which include the use of adhesives or various forms of welding such as solvent welding, hot plate welding, microwave welding, ultrasonic welding or even laser welding.
The plastic pallets made in accordance with the present invention are preferably constructed of a thermoplastic material that allows the pallet to be reused and/or recycled.